1. Field of the Invention
The invention relates to self-adhesive addition-crosslinking silicone compositions and addition-crosslinked silicone elastomers and composite materials prepared therefrom.
2. Background Art
It is known that the adhesion of addition-crosslinked silicone elastomers to numerous substrates, such as plastics, metals and glasses, is poor, i.e. if an addition-crosslinking silicone elastomer material is applied to a substrate and then crosslinked, the silicone elastomer formed can, as a rule, be peeled off the substrate surface without difficulty, for example by applying only small tensile forces. Frequently, spontaneous delamination of silicone elastomers from the substrate may occur. However, since strong and permanent adhesion of the silicone elastomer to the substrate is of decisive importance in numerous applications, a large number of special measures have been proposed for achieving a strong bond between substrates and silicone elastomers.
In principle, the adhesive strength of the silicone elastomer/substrate composite can be increased by suitably changing the chemical and/or physical characteristics of the substrate, or at least its surface, prior to application of the addition-crosslinking silicone elastomer composition. This can be effected, for example, by pretreating the substrate surface with adhesion-promoting additives, so-called primers; by subjecting the substrate surface to plasma treatment; by mixing special additives into the substrate; by selectively adjusting the morphology of the substrate, for example by increasing the surface roughness, etc. These measures have, inter alia, the disadvantage that additional process steps are required or that the characteristics of the substrate have to meet special requirements.
The adhesive strength of the silicone elastomer/substrate composite can also be increased by selectively changing the chemical and/or physical characteristics of the addition-crosslinking silicone elastomer material. Numerous adhesion-promoting additives are known which promote self-adhesion of the resulting silicone elastomer to various substrates when mixed with the uncrosslinked silicone material. These include compounds which contain highly reactive functional groups, such as alkoxy, epoxy, carboxyl, amino, etc., these groups generally being chosen so that the adhesion promoter is capable of reacting both with the substrate and with a silicone elastomer component. Although incorporation of such adhesion promoters may make it possible to dispense with pretreatment of the substrate, the adhesive strength achieved frequently does not meet minimal requirements, in particular where vulcanizing temperatures are limited to less than 100xc2x0 C., important for some applications. In addition, further increases in adhesive strength by employing higher contents of these adhesion promoters is possible only to a limited extent, since the highly reactive groups borne by the adhesion promoters have an increasingly disadvantageous effect on performance characteristics such as shelf-life, crosslinking characteristics (inhibition), toxicological safety, etc. For these reasons, interest has been focused on keeping the content of adhesion promoters as low as possible.
The adhesion promoters most frequently used for self-adhesive addition-crosslinking silicone elastomers are epoxy-functional silanes such as glycidyloxypropyltrimethoxysilane; or methacrylate-functional silanes such as methacryloxypropyltrimethoxysilane; or vinyl silanes such as vinyltrimethoxysilane, or combinations thereof. The organic functional groups relevant for the buildup of composite strength, however, are too unreactive at temperatures below 100xc2x0 C. to bring about sufficient adhesion to the substrate. In the case of many important applications of self-adhesive silicone elastomers, the maximum vulcanizing temperature is limited, one example being the encapsulation of electronic circuits. The temperature-sensitive components such as coils, capacitors, and ICs, permit only very limited thermal loads without risking loss of function. Frequently, only brief heating at temperatures from 50xc2x0 C. to 80xc2x0 C. is possible.
U.S. Pat. No. 5,164,461 and European published application EP-A-451 946 describe addition-crosslinking silicone elastomers with intrinsic adhesion to the substrates that are contacted during vulcanization. The most common adhesion promoters here are epoxide- and/or methacrylate-functional alkoxysilanes. The vulcanizing temperatures are required to be at least 130xc2x0 C. Using the maleate- and fumarate-functional alkoxysilane additives claimed in U.S. Pat. No. 5,164,461, self-adhesion is achieved at crosslinking temperatures of at least 100xc2x0 C.
U.S. Pat. No. 5,595,826 describes adhesion promoters based on reaction products of aliphatically unsaturated monoalcohols or polyalcohols with organofunctional alkoxysilanes such as methacryloxypropyltrimethoxysilane or glycidyloxypropyltrimethoxysilane. Additives of this kind bring about self-adhesion of addition-crosslinking silicone elastomers at vulcanizing temperatures from 70 to 100xc2x0 C. However, high adhesive strengths are achieved exclusively with metallic and inorganic substrates, for example steel, aluminum, glass and copper.
U.S. Pat. Nos. 5,416,144 and 5,567,752 describe adhesion promoters based on reaction products of amines or aminoalkoxysilanes with methacryloxypropyl- or glycidyloxypropyltrimethoxysilane. With these additives, self-adhesion is achieved at vulcanizing temperatures from 80 to 100xc2x0 C. A problem in this case is the strong inhibition on the Pt-catalyzed crosslinking reaction caused by amine compounds, as is well known. Furthermore, contact between amine compounds and SiH components constitutes a potential risk, since formation of hydrogen gas must be expected. Moreover, due to the loss of SiH groups, undervulcanization is expected. A further disadvantage of highly polar additives of this kind is severe thixotroping of the siloxane composition and the associated reduction in fluidity.
EP-A-286 387 describes organosilicon compounds with a xcex2-keto ester function. In particular, alkoxysilanes having at least one alkyl-bonded xcex2-keto ester function are described. Numerous applications of such structures are indicated, including applications as constituents of primers for epoxy resin/glass fiber composites. EP-A-295 657 describes metal chelate complexes formed, for example, from titanium and the chelating ligand, trialkoxysilylpropylacetoacetate. Structures of this kind are claimed to be adhesion-promoting additives in epoxy resin formulations.
U.S. Pat. No. 5,041,481 describes adhesion promoters obtained by the reaction of 1,3-diketone compounds with aminoalkylalkoxy silanes. The latter are claimed, inter alia, to be additives in condensation-crosslinking silicone elastomers. It must be noted that all the adhesion-promoting additives described based on 1,3-diketone compounds necessitate complicated reactions with alkoxysilanes for attachment of alkoxysilyl functionality. Disadvantages in this context are that in some cases, highly toxic reactants such as trimethoxysilane are required. Further, owing to keto/enol tautomerism, a difficult reaction regime is created, with numerous secondary reactions such as propene elimination or reduction of the keto group by SiH groups. Distillative purification and isolation of the reaction products are possible only with massive loss of yield, owing to gellation as a result of the reaction of the enol groups of the 1,3-diketone structure with alkoxysilyl groups with elimination of alcohol. Owing to their known effect of strong inhibition of hydrosilylation, adhesion promoters based on amino-functional alkoxysilanes are of only limited usefulness in addition-crosslinking silicone elastomers.
The present invention pertains to addition crosslinking compositions containing (A), an organopolysiloxane with unsaturated hydrocarbon group functionality; (B), an Sixe2x80x94H functional crosslinker containing compatability decreasing groups; (C), an adhesion promoter containing minimally one aliphatically unsaturated hydrocarbon group and at least one xcex2-diketone or xcex2-ketoester group; and (D) a hydrosilylation catalyst. The particular combination of compatibility-reducing crosslinker (B) and adhesion promoter (C) have a synergistic effect on adhesion. The compositions exhibit excellent adhesion to a variety of substrates without the disadvantages of prior adhesion-promoting additives.
The invention thus relates to self-adhesive addition-crosslinking silicone compositions which contain:
(A) a diorganopolysiloxane of the general formula (1)
R1aR2bSiO(4-a-b)/2xe2x80x83xe2x80x83(1),
in which
R1 is a hydroxyl radical or a monovalent, optionally halogen-substituted C1-20 hydrocarbon radical optionally containing O, N, S or P atoms, and free of aliphatically unsaturated groups,
R2 is a monovalent, aliphatically unsaturated, optionally halogen-substituted C2-10 hydrocarbon radical optionally containing O, N, S or P atoms, and
b is on average from 0.003 to 2, with the proviso that 1.5 less than (a+b) less than 3.0, that on average at least two aliphatically unsaturated radicals R2 are present per molecule, and that the viscosity of the diorganopolysiloxane (A), determined at 25xc2x0 C., is 1 mPaxc2x7s to 40,000 Paxc2x7s;
(B) an organohydrogenpolysiloxane of the general formula (2)
R3cR4dR5eHfSiO(4-c-d-2e-f)/2xe2x80x83xe2x80x83(2),
in which
R3 is a monovalent aliphatically saturated C1-20 hydrocarbon radical, R4 is (a) an optionally halogen-substituted monovalent C6-15 hydrocarbon radical which contains at least one aromatic C6-ring, or
(b) a halogen-substituted, saturated monovalent C2-20 hydrocarbon radical optionally containing O, N, S or P atoms,
R5 is a bivalent, optionally halogen-substituted C6-20 hydrocarbon radical Si-bonded at both ends, optionally containing O, N, S or P atoms, and c, d, e and f denote positive numbers, with the proviso that the relationship: 0.05 less than 100 (d+e)/(c+d+e+f) less than 12 is fulfilled and that the viscosity of the organo-hydrogenpolysiloxane (B), determined at 25xc2x0 C., is 1 mPaxc2x7s to 100 Paxc2x7s;
(C) compounds containing at least one aliphatically unsaturated radical and at least one xcex2-diketone or xcex2-keto ester function, of the general formula (3):
R7xe2x80x94COxe2x80x94CHR8xe2x80x94COxe2x80x94(O)gxe2x80x94R9xe2x80x83xe2x80x83(3),
where
R7 and R9 are each an identical or different,
(a) monovalent, aliphatically unsaturated, optionally halogen-substituted C2-12 hydrocarbon radical, and optionally containing O, N, S or P atoms, or
(b) a monovalent aliphatically saturated C1-20 hydrocarbon radical,
R8 is hydrogen,
(a) a monovalent, aliphatically unsaturated, optionally halogen-substituted C2-12 hydrocarbon radical, and optionally containing O, N, S or P atoms, or
(b) a monovalent aliphatically saturated C1-20 hydrocarbon radical,
g is 0 or 1; and
(D) a hydrosilylation catalyst.
Organohydrogenpolysiloxane (B) acts as an adhesion promoter and simultaneously as a crosslinking agent.
The advantageous properties of the silicone compositions of the present invention include the fact that the self-adhesion is achieved, in part, by a component required by every addition-crosslinking material, namely the SiH-containing crosslinking agent (B), in combination with the xcex2-diketone-functional or xcex2-keto-ester-functional compound (C), it merely being necessary for the SiH crosslinking agent (B) to contain a few groups which reduce compatibility with the other components of the material, especially with the diorganopolysiloxane. These comparability reducing groups are not reactive functional groups, but are preferably phenyl groups, with the result that the toxicological safety of the material, i.e., drinking water approval, BGA/FDA approval is preserved; no vulcanization problems occur; the shelf-life is sufficient; the transparency of the crosslinked silicone elastomer is maintained; and no components which exude or are extractable are added.
The combination of the SiH crosslinking agent (B) having reduced compatibility, with a xcex2-diketone- or xcex2-keto-ester-functional, and alkenyl-functional compound (C), makes it possible, first, to keep the content of incompatible groups in the SiH crosslinking agent low, and secondly, to achieve the adhesion-promoting activity of the xcex2-diketone- or xcex2-keto-ester-functional and alkenyl-functional compound (C) even when employing SiH crosslinking agents with relatively low SiH functionality. Only the combination of the two components (B) and (C) leads to synergistic self-adhesion effects of these two components.
In particular, the present composition is distinguished by the facts that
a) adhesion to a variety of substrates, such as PBT, PA6, PA66, and PPS, as well as steel, aluminum and glass, is achieved at vulcanizing temperatures below 100xc2x0 C.;
b) the crosslinking rate is only minimally affected;
c) the transparency of the crosslinked silicone elastomers is not impaired;
d) there is no need to accept any disadvantageous changes in the mechanical elastomer properties;
e) the adhesion-promoting component (B) simultaneously acts as a crosslinking agent;
f) the fluidity of the uncrosslinked material is minimally reduced; and
g) strong self-adhesion can be achieved even on metals without hindering the deformability from metal vulcanization molds.
In the latter respect, it was found that the adhesion to metal shortly after crosslinking permits demolding of the silicone elastomer part. If, however, the silicone elastomer/metal composite is stored prior to demolding, the silicone elastomer adheres strongly and permanently onto the metal surface within a short time.
Although the adhesion-promoting component (B) of the present invention also has reduced compatibility with the other components of the material, which is evident from turbidity upon admixing, this turbidity disappears completely as soon as the material is heated for the purpose of crosslinking, indicating homogeneous distribution of the molecules of the crosslinking agent in the material at the time of crosslinking.
The second adhesion-promoting constituent, constituent (C) of the present invention, contains a xcex2-diketo function or xcex2-keto ester function. This 1,3-diketone structure is present both in xcex2-diketones and in xcex2-keto esters, such as acetoacetic esters, for example. This 1,3-diketone structure brings about an increase in adhesion at low vulcanizing temperature. Responsibility for this effect is attributed to strong dipolar interactions of the 1,3-diketo function or to hydrogen bonding of the enol form of the additive with polar groups of the substrates. The anchoring of the substrate-interacting xcex2-diketo function into the siloxane network is provided by the aliphatically unsaturated radical, which is amenable to hydrosilylation with the SiH crosslinker. The synergy of the constituents (B) and (C) is believed to reside in the migration behavior of the SiH crosslinker causing an increased concentration of the latter at the siloxane/substrate interface. This migration behavior is believed brought about by the incompatibility of the SiH crosslinker with the siloxane composition, with the result that sufficient SiH crosslinker functionality is present at the laminate interface for the incorporation of the substrate-interacting xcex2-diketo function by hydrosilylative crosslinking, this incorporation by crosslinking believed responsible for the buildup of adhesion.
Each of components (A), (B) and (C) may comprise a single compound or a mixture of different compounds. The terms xe2x80x9caxe2x80x9d and xe2x80x9canxe2x80x9d mean xe2x80x9cone or morexe2x80x9d unless indicated to the contrary.
Examples of the radicals R1 are alkyl radicals such as the methyl, ethyl, propyl, isopropyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, n-octyl, 2-ethylhexyl, 2,2,4-trimethylpentyl, n-nonyl and octadecyl radicals; cycloalkyl radicals such as the cyclopentyl, cyclohexyl, cycloheptyl, norbornyl, adamantylethyl or bornyl radicals; aryl or aralkyl radicals such as the phenyl, ethylphenyl, tolyl, xylyl, mesityl or naphthyl radicals; aralkyl radicals such as the benzyl, 2-phenylpropyl or phenylethyl radicals; and those derivatives of the above radicals which are halogenated and/or functionalized with organic groups, for example the 3,3,3-trifluoropropyl, 3-iodopropyl, 3-isocyanatopropyl, aminopropyl, methacryloyloxymethyl or cyanoethyl radicals. Preferred radicals R1 contain 1 to 10 carbon atoms and optionally halogen substituents. Particularly preferred radicals R1 are the methyl, phenyl and 3,3,3-trifluoropropyl radicals, in particular the methyl radical.
The radicals R2 are obtainable by a hydrosilylation reaction. Examples of these are alkenyl and alkynyl radicals, such as the vinyl, allyl, isopropenyl, 3-butenyl, 2,4-pentadienyl, butadienyl, 5-hexenyl, undecenyl, ethynyl, propynyl and hexynyl radicals; cycloalkenyl radicals, such as the cyclopentenyl, cyclohexenyl, 3-cyclohexenylethyl, 5-bicycloheptenyl, norbornenyl, 4-cyclooctenyl or cyclooctadienyl radicals; alkenylaryl radicals, such as the styryl or styrylethyl radicals; and those derivatives of the above radicals which are halogenated and/or contain heteroatoms, such as the 2-bromovinyl, 3-bromo-1-propynyl, 1-chloro-2-methallyl, 2-(chloromethyl)allyl, styryloxy, allyloxypropyl, 1-methoxyvinyl, cyclopentenyloxy, 3-cyclohexenyloxy, acryloyl, acryloyloxy, methacryloyl or methacryloyloxy radicals. Preferred radicals R2 are the vinyl, allyl and 5-hexenyl radical, in particular the vinyl radicals.
In the case of the diorganopolysiloxanes (A) of the general formula (1), the viscosity determined at 25xc2x0 C. is preferably 100 mPaxc2x7s to 30,000 Paxc2x7s. Most preferably, the viscosity range is from 1 to 30,000 Paxc2x7s. Depending on the type of the addition-crosslinking material, different viscosity ranges are particularly preferred. Viscosities from 100 to 10,000 mPaxc2x7s are particularly preferred for the materials known as RTV-2 (two-component, room temperature vulcanizing); from 1 to 100 Paxc2x7s for LSR (liquid silicone rubber); and from 2000 to 40,000 Paxc2x7s for HTV (high temperature vulcanizing).
Examples of R3 are alkyl radicals such as the methyl, ethyl, propyl, isopropyl, tert-butyl, n-octyl, 2-ethylhexyl or octadecyl radicals, and cycloalkyl radicals such as the cyclopentyl, cyclohexyl, norbornyl or bornyl radicals. Preferred radicals R3 are hydrocarbon radicals having 1 to 10 carbon atoms. A particularly preferred radical R3 is the methyl radical.
Examples of radicals R4 (a) are the phenyl, tolyl, xylyl, biphenylyl, anthryl, indenyl, phenanthryl, naphthyl, benzyl, phenylethyl or phenylpropyl radical, and those derivatives of the above radicals which are halogenated and functionalized with organic groups, such as o-, m- or p-chlorophenyl, pentafluorophenyl, bromotolyl, trifluorotolyl, phenoxy, benzyloxy, benzyloxyethyl, benzoyl, benzoyloxy, p-tert-butylphenoxypropyl, 4-nitrophenyl, quinolinyl or pentafluorobenzoyloxy radicals.
Examples of hydrocarbon radicals R4 (b) having 2 to 20 carbon atoms are the 3-chloropropyl, 3-bromopropyl, 3,3,3-trifluoropropyl, 2-fluoroethyl, 1,1-dihydroperfluorododecyl or 2-cyanoethyl radicals. Particularly preferred radicals R4 are the phenyl radical and the 3,3,3-trifluoropropyl radical.
Preferred radicals R5 correspond to the general formula (4)
xe2x80x94(O)sxe2x80x94(R6)txe2x80x94(O)uxe2x80x94(X)w(O)uxe2x80x94(R6)txe2x80x94(O)sxe2x80x83xe2x80x83(4)
in which
s, t, u and w, independently of one another, denote the values 0, 1 or 2,
R6 may be identical or different and denote a bivalent, optionally halogen-substituted hydrocarbon radical which optionally contains O, N, S or P atoms, is free of aliphatically unsaturated aliphatic groups and contains 1 to 10 carbon atoms, such as xe2x80x94CH2-, xe2x80x94CH2xe2x80x94CH2-, xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2-, xe2x80x94CF2-, xe2x80x94CH2xe2x80x94CF2-, xe2x80x94CH2xe2x80x94CH(CH3)-, xe2x80x94C(CH3)2-, xe2x80x94CH2xe2x80x94C(CH3)2-, xe2x80x94C(CH3)2xe2x80x94CH2-, xe2x80x94CH2xe2x80x94CH2xe2x80x94O- or xe2x80x94CF2xe2x80x94CF2xe2x80x94O-,
xe2x80x94(X)- denotes a bivalent radical which is selected from xe2x80x94Ph-, xe2x80x94Phxe2x80x94Oxe2x80x94Ph-, xe2x80x94Phxe2x80x94Sxe2x80x94Ph-, xe2x80x94Phxe2x80x94SO2xe2x80x94Ph-, xe2x80x94Phxe2x80x94C(CH3)2xe2x80x94Ph-, xe2x80x94Phxe2x80x94C(CF3)2xe2x80x94Ph-, xe2x80x94Phxe2x80x94C(O)xe2x80x94Ph-, cyclohexylene or norbornylene, xe2x80x94Ph- designating a phenylene group. It is preferable that s and u be 0 or 1. A particularly preferred radical R5 is the phenylene radical.
The organohydrogenpolysiloxane (B) preferably contains 5 to 50 SiH groups, in particular 8 to 25 SiH groups, per molecule. The viscosity of component (B), measured at 25xc2x0 C., is preferably 2 mPaxc2x7s to 1 Paxc2x7s. Owing to the labile nature of the SiH group, the component (B) may have a low content, typically less than 100 ppm by weight, of Si-bonded OH groups, arising, for example, from its preparation.
At least one of the radicals R7, R8 and R9 in compound (C) is aliphatically unsaturated and amenable to a hydrosilylation reaction. Examples of aliphatically unsaturated radicals (a) are alkenyl and alkynyl radicals such as vinyl, allyl, isopropenyl, 3-butenyl, 2,4-pentadienyl, butadienyl, 5-hexenyl, undecenyl, ethynyl, propynyl and hexynyl radicals; cycloalkenyl radicals such as cyclopentenyl, cyclohexenyl, 3-cyclohexenylethyl, 5-bicycloheptenyl, norbornenyl, 4-cyclooctenyl or cyclooctadienyl radicals; alkenylaryl radicals such as styryl or styrylethyl radicals, and also halogenated and heteroatom-containing derivatives of the aforementioned radicals, such as vinyloxy, allyloxy, 5-hexenyloxy, 2-bromovinyl, 3-bromo-1-propynyl, 1-chloro-2-methylallyl, 2-(chloromethyl)allyl, styryloxy, allyloxypropyl, 1-methoxyvinyl, cyclopentenyloxy, 3-cyclohexenyloxy, adryloyl, acryloyloxy, methacryloyl or methacryloyloxy radicals. Preferred aliphatically unsaturated radicals are vinyloxy, allyloxy and 5-hexenyloxy radicals, especially the allyloxy radical.
Examples of aliphatically saturated hydrocarbon radicals R7, R8 or R9 (b) are alkyl radicals such as methyl, ethyl, propyl, isopropyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, n-octyl, 2-ethylhexyl, 2,2,4-trimethylpentyl, n-nonyl and octadecyl radicals; cycloalkyl radicals such as cyclopentyl, cyclohexyl, cycloheptyl, norbornyl, adamantylethyl or bornyl radical; aryl or alkaryl radicals such as phenyl, ethylphenyl, tolyl, xylyl, mesityl or naphthyl radicals; aralkyl radicals such as benzyl, 2-phenylpropyl or phenylethyl radicals, and also halogenated or heteroatom-containing derivatives, or derivatives of the aforementioned radicals functionalized with organic groups. Preferred radicals contain 1 to 10 carbon atoms and also, if desired, halogen substituents. Preferred aliphatically saturated radicals are methyl, ethyl, propyl, and butyl radicals. The methyl radical is a particularly preferred radical.
Examples of the radical R8, furthermore, are hydrogen, or an aliphatically unsaturated or aliphatically saturated radical as defined above. A preferred radical R8 is hydrogen.
In the general formula (3), g is preferably 1, i.e., compound (C) is a keto ester. A particularly preferred compound (C) is allyl acetoacetate.
The radicals R1 to R9 in all above formulae may be identical or different. Preferred heteroatoms are N, O and S. Preferred halogen substituents are F, Cl and Br.
Preferably 0.1 to 50 parts by weight, more preferably 0.5 to 10 parts by weight of organohydrogenpolysiloxane (B), and 0.1 to 10 parts by weight, more preferably 0.3 to 3 parts by weight of compound (C) are used per 100 parts by weight of diorganopolysiloxane (A).
The hydrosilylation catalyst (D) serves as a catalyst for the addition reaction, termed hydrosilylation, between the aliphatically unsaturated hydrocarbon radicals R2 of the diorganopolysiloxanes (A) and the silicon-bonded hydrogen atoms of the organohydrogenpolysiloxanes (B). Numerous suitable hydrosilylation catalysts are described in the literature. In principle, all hydrosilylation catalysts corresponding to the prior art and used in addition-crosslinking silicone rubber materials can be used.
Metals and their compounds such as platinum, rhodium, palladium, ruthenium and iridium, preferably platinum, can be used as hydrosilylation catalysts (D). The metals can optionally be fixed on finely divided support materials, such as active carbon, metal oxides, such as alumina, or silica.
Platinum and platinum compounds are preferably used. Particularly preferred platinum compounds are those which are soluble in polyorganosiloxanes. The soluble platinum compounds used may be, for example, the platinum-olefin complexes of the formulae (PtCl2xc2x7olefin)2 and H(PtCl3xc2x7olefin), with preference given to alkenes having 2 to 8 carbon atoms, such as ethylene, propylene, isomers of butene and of octene, or cycloalkanes having 5 to 7 carbon atoms, such as cyclopentene, cyclohexene and cycloheptene. Additional soluble platinum catalysts are the platinum-cyclopropane complexes of the formula (PtCl2C3H6)2, the reaction products of hexachloroplatinic acid with alcohols, ethers and aldehydes and mixtures thereof, or the reaction product of hexachloroplatinic acid with methyl-vinylcyclotetrasiloxane in the presence of sodium bicarbonate in ethanolic solution. Platinum catalysts with phosphorous, sulfur and amine ligands may also be used, e.g. (Ph3P)2PtCl2. Complexes of platinum with vinylsiloxanes, such as symdivinyltetramethyldisiloxane, are particularly preferred.
The amount of hydrosilylation catalyst (D) used depends on the desired crosslinking rate and economic considerations. Preferably 1xc3x9710xe2x88x925 to 5xc3x9710xe2x88x922 parts by weight, in particular 1xc3x9710xe2x88x923 to 1xc3x9710xe2x88x923 parts by weight of platinum catalysts, calculated as platinum metal, are used per 100 parts by weight of diorganopolysiloxanes (A).
The self-adhesive addition-crosslinking silicone compositions can optionally contain further components (E), such as fillers, inhibitors, stabilizers, pigments and catalysts. For the buildup of cohesive adhesion on aluminum and steel substrates, the further addition of organotitanium or organozirconium compounds such as titanium tetrabutylate or zirconium tetrabutylate, for example, is particularly preferred.
In order to achieve sufficiently high mechanical strength of the crosslinked silicone rubber, it is preferable to incorporate actively reinforcing fillers as component (F) into the addition-crosslinking silicone compositions. The actively reinforcing fillers (F) used are in particular precipitated and pyrogenic silicas, and mixtures thereof. The specific surface area of these actively reinforcing fillers should be at least 50 m2/g, and preferably in the range from 100 to 400 m2/g determined according to the BET method. Such actively reinforcing fillers are very well known materials in the area of silicone rubbers.
The compounding of the self-adhesive addition-crosslinking silicone compositions is effected by mixing the abovementioned ingredients in any desired sequence. The crosslinking of the self-adhesive addition-crosslinking silicone compositions is preferably effected by heating, preferably at 30xc2x0 C. to 250xc2x0 C., preferably between 50xc2x0 C. and 80xc2x0 C.
The invention also relates to the addition-crosslinked silicone elastomers prepared from the crosslinkable compositions. The silicone compositions can be bonded to a substrate by applying the silicone compositions to the substrate and then crosslinking them, preferably by heating to 30 to 250xc2x0 C., to give a composite material.
The self-adhesive addition-crosslinking silicone composition can advantageously be used, in particular, where good adhesive strength between the addition-crosslinked silicone elastomer and a substrate, preferably consisting of organic plastics, ie id metals or glasses is desired and the vulcanizing temperature is limited to temperatures of not more than 100xc2x0 C., in particular not more than 80xc2x0 C. The substrate may be present as a shaped article, film or coating.
The self-adhesive addition-crosslinking silicone compositions are suitable for the production of composite materials by coating, adhesive bonding or casting and for the production of shaped articles. The self-adhesive addition-crosslinking silicone compositions are particularly suitable for casting and for adhesively bonding electrical and electronic parts and for the production of composite shaped articles. Composite shaped articles are understood here as meaning a uniform shaped article comprising a composite material which is composed of a silicone elastomer part produced from the silicone compositions and at least one substrate, so that there is a strong, permanent bond between the two parts. Such a composite shaped article is preferably produced by processing an organic plastic to give a shaped article and then bringing the silicone compositions into contact with this shaped article and crosslinking them, which can be effected, for example, by the injection molding method, by means of extrusion and in the so-called press-molding method. Composite materials and in particular composite shaped articles can be used in a very wide range of applications, for example in the electronics, household appliances, consumables, construction and automotive industry, in medical technology, in the production of sport and leisure articles, etc.